In my 1976 Chevy p/u I noticed no plastic aperatous or tube just the hole machined into the transmission casing. My question should there be something to protect it because all I found was a dirt dobbers nest right in it plugging it.

What in the heck is a "dirt dobber?" Doesn't really matter the vent is probably a mushroom looking thing up high pretty sure you can just take that out clean or replace it. Some set ups that could be connected to a hose to a higher level depending on type of truck and expected use and be put back as it was intended not just a hole like you mentioned,

I understand what your talking about Tom a tube or mushroom shaped plastic shape piece up towards the top on the gear selector side of the transmission. Made sure of this looking up on the internet to find the correct location but nothing there but a cloged hole full of dried mud I'm figuring from remains of a dirt daubers nest. Noticed you asked what a dirt dauber was I misspelled it. It sounds like from what you just told me there should be can they fall out knocked or not reinstalled?

Are you sure it's missing or just covered up? I've never had one just fall off they are used in gearcases all around can't say for certain the case must be threaded to put it in as a mushroom type or also ones with a hose to up high such that water doesn't get in. Idea is vent the case when it warms up air on top of oil expands let the air out and back in when it cools not to allow water or dirt in. I would just call the dirt from a mud wasp and probably with a vacuum cleaner knock out the dirt so you catch it and see what you have. IDK - junk or new when you see it or what's missing that belongs start the hunt for one. I suppose if trans has been out they might bust off and extract the threaded part for whole new or good used if allowed. Not pleased about the dirt getting inside do everything to prevent that,

Something has to go and just looked it up with little luck. Showed plastic ones and can see time and heat could be easy to break didn't show well how it's installed. Perhaps just stop by a trans specialty shop and describe what you have it's a super common trans used for decades. They both would know or ask questions and probably have one on hand if plastic it wouldn't take much to break,

Tom I called a local transmission parts supplier that carries these plastic transmission vents for a dollar. Had a conversation with them that these vents are very prone to braking and deteriorating from heating and cooling over time the gentleman also told me they just push in figured like you they would at least would be threaded but apprantly not.

Well it's a deal anyway hope just easy and not part left inside hole. Plastic just doesn't last for stuff like this no surprise it's a stocked cheap item. It there is a sleeve in the hole just bend a super cheap screwdriver #1 flat in a right angle with just propane heat - make those for a lot of things.